Spray drying apparatus



June' 23, 1959 c. F. FISCHER 2,391,611

SPRAY DRYING APPARATUS Filed March ll, 1955 J/ 32 INVENTOR. J2 cu/mzsfff/SCHER 3/ 5 50 BY,

x 32 ATTORNEY nited States Patent I;

, SPRAY DRYING APPARATUS Charles F. Fischer, Jersey City, NJ., assignorto Colgate- Palmolive Company, Jersey City, N.J., a corporation ofDelaware Application March 11, 1955, Serial No. 493,708

4 Claims. c1. 159-4 This invention relates to apparatus for spray dryingsolid-containing liquids or slurries and has particular reference toapparatus adapted to prevent collision of freshly atomized wet particleswith interior walls of spray drying chambers.

Spray drying apparatus usually consists of a drying chamber throughwhich is passed a current of heated drying air into which is atomizedsolid-containing liquid or slurry, so that intimate contact between thedrying air and the minute solid-containing particles is effected withthe result that the particles are dried. Means for separating theresulting dry powder from the moisture laden air is provided either inthe drying chamberitself or apart therefrom. p

The atomization of the solid-containing liquid or slurry is normallycarried out at the top of the drying chamber by any of several meanssuch as centrifugal spinner bowls or high pressure nozzles. From theatomizer, a stream of wet particles flows downwardly and outwardly,generally forming a conical orparabolic body until restricted by theinterior of the drying chamber. The particular size and shape of thecone obtained under any one set of conditions is a complex function ofmany variables. However, as a result of their outward flow, at leastsome of the particles normally collide with the inner vertical walls ofthe drying chamber, and frequently some particles adhere thereto. Thisproblem is especially acute at the upper part of the drying chamberwhere the materials striking the wall of the chamber are wet andplastic, having been subjected to a minimum of drying action. Under suchconditions, deposits of solids accumulate on the interior of the chamberwall, and because of their extended exposure to high temperatures,usually char and/ or decompose. These deposits accumulate until theyfall of their own weight and then the cycle is repeated.

Various means have been proposed to overcome this difficulty. Thus thediameter of the drying chamber may be enlarged or an atomizer may beemployed which disperses particles within a relatively narrow angle ofdispersion. However, enlarging the chamber is expensive and diminishingthe angle encompassed by the cone of atomized material reduces theamount of material which a drier can process within a given period oftime.

A means has now been discovered to facilitate the use of atomizershaving a wide angle of dispersion in a drying chamber of moderate orrelatively small diameter without experiencing substantial collision ofwet particles with the wall under a wide range of operating conditions.In accordance with the present invention such improved spray dryingapparatus comprises a drying chamber, defined in part by a substantiallyvertical wall, means for dispersing material to be dried in said chamberas a paraboloid of wet particles which, if unimpeded, would collide withsaid substantially vertical wall of said chember, and vertically movablemeans disposed within said chamber for directing a flow of gas inwardlyand downwardly against the upper surface of said paraboloid to Fig. 1 isan elevation of the upper portion of a spray drying apparatus equippedwith two independently vertically movable systems of air jets,

Fig. 2 is a detailed drawing, on an enlarged scale, of a portion of oneof the systems of vertically movable air jets of Fig. 1, and

Fig. 3 is a plan view of the elevating drive mechanism of Fig. 2 and istaken along a line 33 of Fig. 2..

Referring now to Fig. 1 of the accompanying drawing, the illustrativespray drier comprises a drying chamber 16 defined by a cylindrical shellor wall 18. A truncated conical, cover 20 encloses the top of thecylindrical shell 18. At the apex of the cover 20 is a duct 22 leadingto a supply of heated drying air (not shown). Centrally disposed nearthe top of the chamber is a whirling disc atomizer 26 which communicateswith the exterior of the chamber by means of a conduit 28.

Secondary manifolds 31, carrying air jets 32, are mounted adjacent tothe chamber wall 18. These secondary manifolds are supported by conduits38 mounted on primary manifolds 40 which are supported by elevatingstruts .42 slidably mounted in stationary guide arms 46 affixed to thechamber Wall 18 or other supporting means (not shown) so as to locatethe air jet system adjacent to the chamber wall 18 and just above theupper surface of the coneof wet particles 44. Afiixed to each of thestruts 42 is a rack 47 which is enmeshed with a pinion gear 48. Flexibleconduits50, aifixed to the main manifolds. 40 by, nipples 51 and unions52, communicate the mainmanifolds 40 with an air supply system exteriorof the chamber (not shown).

Referring now to Fig. 2 for details of a portionof the upper of the twoair jet systems, the air jets 32 comprise small, hollow nozzles weldedto the three secondary manifolds 31 around suitable openings for flow ofgas from the manifold through the nozzles. The nozzles or jets have axesdirected radially inwardly and downwardly. The secondary manifolds 31are supplied with air from the primary or main manifold 40 throughconduits38, the main manifold being supported by an elevating strut 42to which is aflixed a rack 47 engaging a pinion gear 48. The elevatingstrut 42 passes through a sleeve bearing 56 in the stationary guide arm46.

The pinion gear 48 is driven by rotation of a worm gear 58 which ismounted on a drive shaft 60 adapted to be rotated by a handwheel 62. Twosleeve bearings, 64 and 66, which retain and position the drive shaft60, are supported in one case (64) directly by the chamber wall and inthe other (66) by a bracket 68 which is in turn afi'ixed to the chamberWall. Also supported by the bracket 68 is the pinion gear 48.

In operation, flow of drying air into the chamber via the duct 22 isinitiated and the handwheels 62 are rotated to position the air jetsystems at elevations known or expected to be suitable for use under theproposed conditions of operation. Air, preferably heated so as to exertsome drying influence, is supplied to the jets 32, and drying ofsolid-containing liquid is initiated by pumping slurry to the rotatingwhirling disc atomizer 26 through the conduit 28. The air from the jets32 blasts inwardly and downwardly against the periphery of the parabolicbody of wet particles 44 to diminish the horizontal diameter thereof andthereby prevent the contact of wet particles with the chamber wall 18which would otherwise normally occur.

After reaching equilibrium spraying conditions, the handwheels 62 arerotated so as to position the air jet systems at the optimum elevationfor preventing substantial buildup of wet particles on the chamberwalls. This position is best determined by routine experiments, but maybe established to a certain extent by visual observation of the interiorof the chamber wall by means of portholes (not shown) in the chamberwall and/or conical cover.

While the preferred embodiment which has been illustrated utilizesconcurrent flow of drying air and wet solids, i.e., both traveldownwardly through the chamber, it is possible, although not assatisfactory, to employ the instant invention in spray drying apparatuswherein drying air passes upwardly through the chamber countercurrentlyto the downward flow of atomized particles.

From the foregoing it will be seen that the present invention provides adevice which is simple and flexible in operation and which faciltatesthe production of spray dried products of high quality under widelyvarying conditions.

While there has been shown what is at present considered to be thepreferred embodiment of the invention it will be understood, of course,that many modifications and changes may be made therein withoutdeparting from the true spirit of the invention which is to be accordedthe full range of equivalents comprehended by the accompanying claims.

Having thus described the invention, what is deemed to be secured byLetters Patent is:

1. Spray drying apparatus adapted for both concurrent and countercurrentflow of drying air and material to be dried comprising a drying chamberdefined in part by a substantially vertical wall, a gas conduit fordrying air having unimpeded access to the top of said drying chamber,means for dispersing material to be dried in said chamber as aparaboloid of wet particles which, if unimpeded, would collide with saidsubstantially vertical wall of said chamber, bodily vertically movablemeans for directing a flow of gas inwardly and downwardly against theupper surface of said paraboloid to diminish the diameter thereof andthereby prevent contact of said wet particles with said wall of saiddrying chamber during drying by either concurrent or countercurrent flowof said drying air and said material to be dried, and means forsupporting said bodily vertically movable means within said chamberbeneath said dispersing means.

2. Spray drying apparatus adapted for both concurrent and countercurrentflow of drying air and material to be dried comprising a drying chamberdefined in part by a substantially vertical wall, a gas conduit fordrying air having unimpeded access to the top of said drying chamber,means for dispersing material to be dried in said chamber as aparaboloid of wet particles which, if unimpeded, would collide with saidwall of said chamber, bodily vertically movable means for directing aflow of gas inwardly and downwardly against the upper portion of saidparaboloid to limit the diameter thereof during drying by eitherconcurrent and countercurrent flow of said drying air and said materialto be dried, means for supporting said bodily vertically movable meanswithin said chamber immediately beneath said dispersing means andadjacent to said drying chamber Wall, and a flexible conduitcommunicating with said bodily vertically movable means and adapted tosupply gas under pressure thereto.

3. Spray drying apparatus adapted for both concurrent and countercurrentflow of drying air and material to be dried comprising a drying chamberdefined in part by a substantially vertical wall, a gas conduit fordrying air having unimpeded access to the top of said drying chamber,means for dispersing material to be dried in said chamber as aparaboloid of wet particles which, if unimpeded, would collide with saidwall of said chamber, a vertically movable manifold having a pluralityof orifices having axes directed inwardly and downwardly so as to directa stream of gas against the upper surface of said paraboloid to diminishthe diameter thereof and thereby prevent contact of wet particles withsaid wall of said drying chamber during drying by either concurrent orcountercurrent flow of said drying air and said material to be dried, aflexible conduit communicating with said manifold and adapted to supplygas under pressure thereto, and means for supporting said manifold belowsaid dispensing means and adjacent to said drying chamber wall and justabove the normal upper surface of said unmodified paraboloid.

4. Spray drying aparatus as set forth in claim 3 wherein there isdownward flow of said wet particles and of drying air.

References Cited in the file of this patent UNITED STATES PATENTS1,028,267 Osborne June 4, 1912 1,374,555 Dick Apr. 12, 1921 1,594,065MacLachlan July 27, 1926 2,035,673 Schultz Mar. 31, 1936 2,144,098 BakerJan. 17, 1939 2,396,689 Davis Mar. 19, 1946 2,460,546 Stephanofi Feb. 1,1949 2,703,139 Rappleyea Mar. 1, 1955

